Separate writeScalarStream to methods which handle either encrypted or plain streams.

Reading writeScalarStream in Request class,
I found it would be possible to separate this method to two methods,
one is for encrypted stream and another is for plain,
because original writeScalarStream hardly share code for encrypted and for plain.

Separating this method will help me to realize DERBY-1301 separatingly for encrypted and plain,
as I planned in http://issues.apache.org/jira/browse/DERBY-1301#action_12417684 .